1) Field of the Invention
The present invention relates to a gas turbine combustor for a gas turbine. More particularly, this invention relates to a fuel injection nozzle for a gas turbine combustor that supplies fuel to air guided to the gas turbine combustor for the gas turbine, a gas turbine combustor that has this fuel injection nozzle, and a gas turbine that has the nozzle.
2) Description of the Related Art
A conventional gas turbine combustor has widely used a diffusion combustion system that injects fuel and combustion air from different nozzles, and burns the mixture. However, recently, in place of the diffusion combustion system, a premixed combustion system which is advantageous based on a reduction of thermal NOx has come to be used. The premixed combustion system refers to a system that mixes fuel and combustion air in advance, injects the mixture (hereinafter, “premixed gas”) from one nozzle, and burns the mixture. According to this premixed combustion system, even if the ratio of the fuel to the premixed gas is low, the premixed gas is burned in all the combustion area. Therefore, it is easy to lower the temperature of the flame (hereinafter, “premixed flame”) generated by the premixed gas. Consequently, this system is advantageous in the reduction of NOx as compared with the diffusion combustion system. On the other hand, this system has a problem in that the stability of combustion is inferior to that of the diffusion combustion system, and backfire and autoignition of the premixed gas occur.
FIG. 24 is a cross-sectional view in an axial direction that illustrates one example of a gas turbine combustor based on the premixed system. FIGS. 25A and 25B are diagrams to explain about a main fuel injection nozzle for the gas turbine combustor based on the premixed system used conventionally. Gas turbine combustor internal cylinders 20 are provided at constant intervals within a gas turbine combustor external cylinder 10. A diffusion flame formation corn 30 that stabilizes a premixed flame by forming a diffusion flame is provided at the center of each gas turbine combustor internal cylinders 20. The diffusion flame formation corn 30 forms the diffusion flame by reacting pilot fuel supplied from a pilot fuel injection nozzle 31 with combustion air supplied from between the gas turbine combustor external cylinder 10 and the gas turbine combustor internal cylinders 20.
A premixed flame formation nozzle 40 is provided around the diffusion flame formation corn 30 in advance. A main fuel injection nozzle 610 that injects main fuel, mixes the main fuel with the combustion air, and forms the premixed gas is provided inside the premixed flame formation nozzle 40. This main fuel injection nozzle 610 has a conical shape at a front end thereof. Fuel injection holes 61 that inject the main fuel are provided on the external surface of the main fuel injection nozzle 610. The main fuel injected from the fuel injection holes 61 is mixed with the combustion air supplied from between the gas turbine combustor external cylinder 10 and the gas turbine combustor internal cylinders 20, and the premixed gas is formed. This premixed gas is injected from the premixed flame formation nozzle 40 to a combustion chamber 50 via a premixed flame formation nozzle extension pipe 400.
A high-temperature combustion gas emitted from the diffusion flame ignites the premixed gas injected to the combustion chamber 50, thereby to form the premixed flame. The diffusion flame formed by the diffusion flame formation corn 30 stabilizes the premixed flame. A high-temperature and high-pressure combustion gas is emitted from the premixed flame. The combustion gas passes through a tailpipe, not shown, of the gas turbine combustor, and is guided to a turbine first stage nozzle.
As the above main fuel injection nozzle 610 is provided with the fuel injection holes 61 that inject the main fuel on the external surface of the main fuel injection nozzle 610, the main fuel is injected out along the surface of the main fuel injection nozzle 610. Therefore, this main fuel does not diffuse easily at the downstream, and there is a problem that it is not possible to homogeneously generate the premixed flame. In order to solve this problem, Japanese Patent Application Laid-open No. 6-2848 discloses a fuel injection nozzle that has a plurality of cylindrical spokes having a plurality of fuel injection holes in a radial direction of the fuel injection nozzle, and injects the fuel from the fuel injection holes provided on the spokes. FIG. 26A and FIG. 26B are diagrams to explain about the fuel injection nozzle according to this prior art.
A fuel injection nozzle 620 injects the fuel from the fuel injection holes 61 provided on cylindrical hollow spokes 68. Therefore, there is an advantage that it is easy to diffuse the fuel at the downstream of the hollow spokes 68, and that it is possible to keep a homogeneous and stable combustion state. However, as each hollow spoke 68 has a circular cross section, the flow of the combustion air is disturbed at the back of the hollow spoke 68, which has caused the occurrence of backfire.